In certain aspects, the present invention may be regarded as an improvement over the invention disclosed and claimed in the U.S. patent of John P. Walters, No. 3,749,975, issued July 31, 1973 and assigned to the assignee of the present application. Other background patents of general interest are the Walters and Bernier U.S. Pat. No. 3,973,167, issued Aug. 3, 1976; and the Walters and Coleman U.S. Pat. No. 4,055,783, issued Aug. 25, 1977. Another background disclosure is contained in the U.S. patent application of John A. Bernier, entitled High Voltage Spark Source.